Combustion furnace control apparatus

ABSTRACT

A combustion furnace control apparatus for which an operation control system that ensures the combustion safety of the combustion furnace can be constructed easily. Interlocks pertaining to the safe operation of a combustion furnace are classified as a 1 st  interlock pertaining to the safe operation of the overall combustion furnace, a 2 nd  interlock pertaining to the combustion environment of a combustion zone and a 3 rd  interlock pertaining to the combustion of a burner. Whereby, a common control module judges the state of the 1 st  interlock and controls the overall operation of the combustion furnace; a combustion zone control module, receiving a control signal from the common control module, operates to judge the state of the 2 nd  interlock and prepare the combustion environment for the combustion zone; and a burner control module, receiving a control signal from the combustion zone control module, operates to judge the state of the 3 rd  interlock and control the operation of the burner.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application claims priority under 35 U.S.C. §119 to Japanese Patent Application No. 2009-138117, filed Jun. 9, 2009, which is incorporated herein by reference.

TECHNICAL FIELD

This invention relates to a combustion furnace control apparatus wherein a combustion control system, which conforms to the combustion furnace specifications, guarantees the combustion safety (safe operation) and can be constructed easily.

BACKGROUND OF THE INVENTION

The operation control (combustion control) of a combustion furnace is basically carried out by monitoring the flame of a burner provided in the combustion furnace, the temperature inside the furnace and the composition of exhaust gas from the combustion furnace while using a combustion control apparatus (burner control unit) to control the amount of fuel and the amount of air supplied to the burner (see Kokai (unexamined patent publication) No. 11-118150 (“JP '150”) and Kokai (unexamined patent publication) No. 10-332143 (“JP '143”), for example). Also, when operating the combustion furnace, operation control that ensures (guarantees) the safety of the burner combustion as well as the safety of the combustion furnace operation is implemented by pre-ventilating the inside of the furnace (purge control) and then igniting the burner (ignition control).

In a medium and large size combustion furnaces, however, a plurality of burners are provided inside the furnace, and the inside of the furnace is separated into multiple combustion zones, with one or a plurality of burners provided for each of these combustion zones. Even in such a case, in order to ensure the combustion safety of the combustion furnace, it is important that various interlock, purge completion and other such signals be fed reliably to a plurality of combustion control devices (burner control units) for controlling the combustion (flame) of each burner. For this reason, in an operation control system constructed according to the combustion furnace specifications, measures must be implemented to enable the reliable transmission of the aforementioned interlock, purge completion and other such signals to the combustion control devices (burner control units) that are provided in correspondence to the burners.

Incidentally, typical operation control can be realized easily with sequence control using a programmable logic controller (PLC), for example. In the case of the operation control of a combustion furnace, however, in order to guarantee combustion safety, such usage of a PLC is permitted only if, for example, a general-purpose PLC is configured with custom software pertaining to an interlock for combustion safety. In other words, the configuring of an interlock for combustion safety and controlling of a plurality of combustion control devices (burner control units), without interfacing to an interlock device other than the aforementioned PLC that has been configured with custom software, is prohibited.

Accordingly, when controlling the operation of a combustion furnace, signals pertaining to combustion safety, particularly the interlock and purge completion signals, must be transmitted via safety devices that guarantee safety. For this reason, the configuration of an operation control system constructed according to the combustion furnace specifications typically becomes complex and expensive, and this is an undeniable problem.

The present invention was devised in consideration of this type of situation, and an object of the present invention is to provide a combustion furnace control apparatus whereby an operation control system that conforms to the combustion furnace specifications can be constructed easily and the combustion safety (safe operation) can be guaranteed with certainty.

SUMMARY OF THE INVENTION

To achieve the aforementioned object, the present invention is characterized as modularizing such basic functions as the judging of the state of an interlock pertaining to combustion safety and the monitoring of purge time, and combining these modules so as to enable the construction of an operation control system for combustion furnaces of various specifications. In particular, the interlock signals required for operation of each module are fed directly to the respective modules and, among the modules, control signals such as signals indicating purge completion, for example, are transmit directly so that signals pertaining to combustion safety can be handled without passing through a general-use PLC.

Thus, the combustion furnace control apparatus of the present invention is characterized as comprising a common control module for verifying the state of a 1^(st) interlock pertaining to the safe operation of the entire combustion furnace, outputting common control signals required for the safe operation of the combustion furnace, and controlling the overall operation of the combustion furnace; and a combustion zone control module, provided in correspondence to a combustion zone provided with a burner, for verifying the state of a 2^(nd) interlock pertaining to the combustion environment in the combustion zone and common control signals outputted from the common control module, and controlling the operation of the burner in the combustion zone; wherein the common control module and the combustion zone control module are provided in a hierarchical configuration.

Moreover, another combustion furnace control apparatus of the present invention is characterized as comprising a common control module for verifying the state of a 1^(st) interlock pertaining to the safe operation of the combustion furnace, outputting common control signals required for the operation of the combustion furnace, and controlling the overall operation of the combustion furnace; a combustion zone control module, provided in correspondence to a combustion zone provided with a burner, for verifying the state of a 2^(nd) interlock pertaining to the combustion environment in the combustion zone and common control signals outputted from the common control module, controlling the safe operating environment of the combustion zone, and outputting combustion zone control signals required for operation of the burner provided in the combustion zone; and a burner control module, provided in correspondence to the burner, for verifying the sate of a 3^(rd) interlock pertaining to inherent safe operation in the burner and combustion zone control signals outputted from the combustion zone control module, and for controlling the operation of the burner; wherein the common control module, combustion zone control module and burner control module are provided in a hierarchical configuration.

Incidentally, the combustion furnace comprises a plurality of combustion zones each of which is provided with one or a plurality of burners, for example, and the common control module outputs signals, as the common control signals, for enabling or disabling the operation of a burner provided in the combustion furnace. Furthermore, the combustion zone control module, provided in correspondence to each combustion zone, is configured such that, for example, when the burner operation is enabled, the combustion zone control module ventilates the combustion zone, prepares a safe operating environment for the burner in the combustion zone, and after the safe operating environment of the combustion zone has been prepared, outputs the combustion zone control signals. Also, a burner control module is provided in correspondence to each burner.

Also, combustion control of the burner is implemented by a combustion control device provided in correspondence to the burner, and only when a combustion zone control signal has been received from the combustion zone control module and operation has been enabled, or only when operation has been enabled by a burner control module that has verified a combustion zone control signal from the combustion zone control module and the state of a 3^(rd) interlock, the burner is operated according to combustion control implemented by the combustion control device.

According to a combustion furnace control apparatus having the above mentioned configuration, a plurality of interlocks pertaining to safe combustion are classified as a 1^(st) interlock pertaining to the safe operation of the overall combustion furnace, a 2^(nd) interlock pertaining to the combustion environment of a combustion zone, and a 3^(rd) interlock pertaining to inherent safe operation in the burner; while control modules for monitoring each of the abovementioned interlocks and controlling operation of the combustion furnace are separated into a common control module for controlling the overall operation of the combustion furnace, a combustion zone control module for controlling the safe operation environment of a combustion zone, and a burner control module for controlling the operation of a burner; and each of these modules are constructed hierarchically in accordance with the specifications of the combustion furnace.

Thus, the combustion control system can be constructed easily since each control module simply verifies the state of the corresponding 1^(St) to 3^(rd) interlock of that hierarchical level, performs its operation, and then transmits a control signal to the control module of the next hierarchical level. Furthermore, interlock signals are not transmitted among the modules, but instead acknowledge signals, such as a purge complete signal, for example, are simply transmit directly and therefore the combustion safety (safe operation) can be guaranteed with certainty. Accordingly, a combustion control system conforming to the specifications of the combustion furnace can be constructed inexpensively while ensuring the combustion safety.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic diagram of a combustion control system in a combustion furnace control apparatus according to one embodiment of the present invention.

FIG. 2 shows the configuration of signal transmission between modules.

FIG. 3 is a timing diagram of the operating state during normal operation.

FIG. 4 is a timing diagram of the operating state during an abnormality when the common contact and normally-open contact of a relay are fused together.

FIG. 5 is a timing diagram of the operating state during an abnormality when the common contact, normally-open contact and normally-closed contact of a relay are fused together.

DETAILED DESCRIPTION OF THE INVENTION

The combustion furnace control apparatus of the present invention is described below with reference to drawings.

FIG. 1 shows a schematic diagram of an operation control system in a combustion furnace control apparatus for controlling the operation of the combustion furnace. The combustion furnace basically has a furnace in which combustion zones are provided with one or a plurality of burners. Furthermore, in conformance with the combustion furnace specifications, the interior of the furnace is partitioned into a plurality of combustion zones, and each combustion zone may be provided with one or a plurality of burners. Also, provided in each combustion zone is a ventilation apparatus for ventilating (purging) the interior of the furnace.

FIG. 1 shows a combustion furnace 10, and incidentally, in this example, the interior of the furnace is portioned into three combustion zones, A, B and C, with a plurality of burners (combustion devices) 11 and a ventilation apparatus 12 provided in each combustion zone A, B, C. Moreover, although not expressly shown here, in the combustion furnace 10 is provided a flame sensor for each burner 11 for sensing the flame of the burner 11, and in each combustion zone A, B, C is provided a temperature sensor for sensing the temperature inside the furnace and a pressure sensor for sensing the gas pressure inside the furnace.

A combustion furnace control apparatus for controlling operation of this type of combustion furnace is basically configured to control the combustion of each burner 11 while monitoring various types of interlocks pertaining to the safe operation of the combustion furnace. Moreover, the combustion control for burner 11, as disclosed in the aforementioned JP '150 and JP '143, is implemented by means of a combustion control device (burner control unit: BCU) 13, provided in correspondence to each burner 11, that controls the amount of fuel and the amount of air supplied to the burner 11 while monitoring the flame of each burner 11, the temperature inside the furnace, and the composition of exhaust gas from the furnace.

Namely, the combustion control apparatus of the present invention implements combustion control for each burner 11 while monitoring each interlock, and in particular, the modularization of such basic functions as the judgment of an interlock pertaining to the combustion safety of burner 11 and the monitoring of purge time, and the hierarchically combination of these modules in accordance with the specifications of the combustion furnace 10 enable the construction of an operation control system for combustion furnaces 10 of various specifications. In particular, the interlock signals required for operation of each module are fed directly to the respective module and, among the modules, control signals (acknowledge signals) such as signals indicating purge completion, for example, are transmit directly and reliably with their safety guaranteed so that signals pertaining to combustion safety can be handled without passing through a non-safety device.

Thus, in the apparatus of the present invention, the interlocks pertaining to safe operation of the combustion furnace 10 are classified and handled as a 1^(st) interlock pertaining to safe operation of the entire combustion furnace, a 2^(nd) interlock pertaining to the combustion environment of each of the combustion zones A, B and C, and a 3^(rd) interlock pertaining to operation of each of the burners 11. Namely, each interlock is classified hierarchically as either a 1^(st) interlock pertaining to operation of the entire combustion furnace, a 2^(nd) interlock pertaining to operation of individual combustion zones, or a 3^(rd) interlock pertaining to operation of the individual burners.

Specifically, the aforementioned 1 ^(st) interlock indicates whether the operating conditions of the combustion furnace 10 are favorable, and is comprised of a vibration sensor output, a fire detector output, a power overload output that indicates the results of the monitored power usage, and the like. Additionally, the 2^(nd) interlock indicates whether the combustion environment of the burner 11 in each combustion zone A, B and C is favorable, and is comprised, for example, of a furnace interior high temperature limit interlock whose operation is determined based on the furnace interior temperature, a furnace interior gas pressure interlock, and the like. Furthermore, the 3^(rd) interlock indicates whether the combustion (ignition) conditions for each burner 11 are favorable, and is comprised, for example, of a fuel pressure build-up interlock, a fuel-air pressure low limit interlock, and the like.

Meanwhile, the operation control system that controls the operation of each burner 11 is comprised of a hierarchically connected configuration of a common control module 14 for judging the state of the aforementioned 1 ^(st) interlock and controlling the overall operation of the combustion furnace, combustion zone control modules 15 for judging the state of the 2^(nd) interlock for each combustion zone and controlling the combustion environment (operation conditions) of the respective combustion zones, and burner control modules 16 for judging the state of the 3^(rd) interlock for each burner and controlling the combustion (operation) of the respective burners.

Incidentally, the common control module 14 forms the root of the combustion control system, and is comprised of an interlock judging unit 14 a that judges the state of the 1^(St) interlock, and a purge control unit 14 b that receives the output (combustion furnace operation enable signal) from the interlock judging unit 14 a, designates the initial purge process for the interior of the combustion furnace 10, implements timer control of the initial purge process and outputs a purge completion acknowledge signal (common control signal). In the common control module 14, if a portion of the 1^(st) interlock were to disappear, then operating conditions of the combustion furnace would not be satisfied, of course, and the outputting of the acknowledge signal (common control signal) would be halted.

Specifically, the interlock judging unit 14 a, when an activation signal has been inputted thereto, acknowledges that all interlock signals for the entire furnace are normal and outputs a global purge start enable signal. If an abnormality occurs in the interlock signal, the interlock judging unit 14 a halts the outputting of the global purge start enable signal. Then, the purge control unit 14 b receives the global purge start enable signal and begins the purging process for all of the zones A, B and C (the entire furnace), implements timer control for a preset purge process time, and after a certain purge process time has elapsed, outputs a zone activation signal to each zone A, B and C. Moreover, in the case where the inputting of the global purge start enable signal has been halted, the purge control unit 14 b halts the outputting of a zone activation signal to each of the zones A, B and C, and as a result, the purge process for the entire combustion furnace and the operation of the combustion furnace are halted.

Also, the combustion zone control modules 15 are provided for the combustion zones, and are configured so as to operate only when fed an acknowledge signal (common control signal) from the common control module 14, or more specifically, the zone activation signal). In particular, the combustion zone control module 15 is comprised of an interlock judging unit 15 a that judges the state of the 2^(nd) interlock when fed the zone activation signal and a purge control unit 15 b that receives the output (combustion furnace operation enable signal) from the interlock judging unit 15 a and designates a purge process in the combustion zone, and that implements timer control of the purge process and outputs a purge completion acknowledge signal (combustion zone control signal). In the combustion zone control module 15, if the acknowledge signal (common control signal) from the common control module 14 disappears or a portion of the 2^(nd) interlock disappears, then operating conditions of the combustion furnace would not be satisfied, of course, and the outputting of the acknowledge signal (combustion zone control signal) would be halted.

Specifically, the interlock judging unit 15 a, when a zone activation signal has been inputted thereto, acknowledges that all 2^(nd) interlock signals pertaining to the relevant zone are normal, and outputs a purge start enable signal for that combustion zone. If an abnormality occurs in a 2^(nd) interlock signal, the interlock judging unit 15 a halts the outputting of the purge start enable signal. Then, the purge control unit 15 b receives the zone purge start enable signal and begins the purging process for the relevant combustion zone, implements timer control for a preset purge process time, and after a certain purge process time has elapsed, outputs a combustion activation signal to the burner in the relevant combustion zone. Moreover, in the case where the inputting of the zone purge start enable signal has been halted, the purge control unit 15 b halts the outputting of the combustion activation signal, and as a result, the burner operation is halted.

Also, a burner control module 16 is provided in correspondence to each burner, and is configured so as to operate only when an acknowledge signal (control signal), i.e., the combustion activation signal, is fed from the combustion control zone control module 14. Specifically, the burner control module 16 is comprised of an interlock judging unit 16 a that judges the state of the 3^(rd) interlock, and the combustion control device (burner control unit: BCU) 13 that receives the output (combustion furnace operation enable signal) from the interlock judging unit 16 a and controls the burner combustion. Also in the burner control module 16, if the acknowledge signal (combustion zone control signal) from the combustion zone control module 15 were to disappear or a portion of the 3^(rd) interlock were to disappear, the operation conditions for the combustion furnace would not be satisfied, of course, and the burner control module 16 would halt operation (combustion) of the burner 11.

Specifically, the interlock judging unit 16 a, when a combustion activation signal is inputted thereto, acknowledges that all 3^(rd) interlock signals pertaining to the burner are normal and outputs an ignition signal for the respective burner. However, if an abnormality occurs in the interlock signal, the outputting of the ignition signal is halted. The burner control unit 13 receives the ignition signal from the interlock judging unit 16 a, ignites the burner and controls that combustion while monitoring the combustion status. Moreover, if the ignition signal is disrupted, the burner control unit 13 halts the burner combustion.

Moreover, FIG. 1 only shows the operation control system for combustion zone A as being configured by a hierarchical connection of control modules 14, 15 and 16, but a similar operation control system having a hierarchical relationship may also be configured, of course, for combustion zones B and C. Also, in the case of a simple type of combustion furnace without a 3^(rd) interlock, as shown in combustion zone B, the operation control system may also be configured with only the common control module 14 and the combustion zone control module 15 connected hierarchically, and using the acknowledge signal (combustion zone control signal) from the combustion zone control module 15 so as to control directly the operation of the combustion control device (burner control unit: BCU) 13 provided for each burner 11. In this case, the purge control unit 15 b of the combustion zone control module 15 may be configured to output the burner ignition signal instead of the combustion activation signal. Also, as shown in the combustion zone C of FIG. 1, in the case where there is no zone purge, the operation control system may also be configured such that each burner control unit 13 receives the zone activation signal, ignites the respective burner, and controls the combustion thereof while monitoring the combustion status.

Thus, as described above, with a combustion furnace control apparatus in which the operation control system is configured by connecting a plurality of control modules 14, 15 and 16 hierarchically, the operation control in each control module 14, 15 and 16 may be implemented by directly inputting only the required interlock signals and simply making judgments based thereon, without transmitting the interlock signals to another control module. Moreover, among the hierarchically connected control modules 14, 15 and 16, it is sufficient to transmit directly only the acknowledge signals (common control signals/combustion zone control signals) that indicate operation completion, and therefore, the use a programmable logic controller (PLC), for example, to control sequentially the operation of the combustion furnace with software is unnecessary. In other words, while control signals are transmitted directly among the control modules 14, 15 and 16 that have been constructed using safety devices, the combustion furnace operation can be controlled by judging the state of the interlock at each hierarchical level, and therefore the operational safety of the combustion furnace can be guaranteed easily and efficiently without the use of a general-purpose programmable logic controller (PLC).

Also, since a PLC is not used with this apparatus, there is no need to consider abnormalities that may occur in the PLC itself. Also, if an abnormality occurs in any one of the interlocks, because the control module that judges the state of that interlock can quickly and reliably detect the abnormality, this embodiment provides the effect, among others, of enabling measures to be taken quickly according to the type of abnormality. Moreover, since there is no need to develop custom software for using a PLC, this embodiment has the advantage of enabling the combustion furnace control apparatus to be constructed easily.

Below, the transmission of acknowledge signals among the aforementioned control modules will be explained briefly. FIG. 2 shows example configurations of the transmission-side module and reception-side module that accomplish the transmission of acknowledge signals among the control modules.

The transmission-side module is equipped with two parallel control devices (CPUs), 1 a and 1 b, in the common control module 14 for example, that generate pulses of a certain fixed period and enhance the reliability of the acknowledge signals (pulse signals) by generating multiple (doubly redundant) information (pulse signals) indicating the presence of the acknowledge signals (common control signals) or interlock signals. Incidentally, control devices (CPUs) 1 a and 1 b usually operate in synchronization with each other and function as signal generators for generating time division pulse signals. Specifically, the control devices (CPUs) 1 a and 1 b are configured so as to generate alternately at 100 ms intervals, for example, pulse signals having a 20 ms cycle and forming a square wave with a 50% duty cycle. Then, the respective pulse signals outputted from each of the control devices (CPUs) 1 a and 1 b pass through a logical OR circuit (pulse signal synthesis unit) comprised of transistors 2 a and 2 b and are combined into a single signal which, as a pulse signal (pulse signal string) that is continuous with a certain fixed cycle in a time-series, is output through an output transistor 3 to the combustion zone control module, which is the reception-side module.

Moreover, a relay (switch) 4 for controlling the external outputting of the pulse signals outputted from the output transistor 3 is inserted in series into the output stage of the common control module 14, and pulse signals (acknowledge signals) are output externally via a normally-open contact NO only when this relay 4 is on (when in a driving state). Specifically, the relay 4 is a switching type relay, and when an electromagnetic coil L thereof is in a non-conducting (off) state, a common terminal C is connected to a normally-closed contact NC side, and when the electromagnetic coil L is in a conduction driving (on) state, the common terminal C is connected to the normally-open contact NO side. In this embodiment, the common contact C of the relay 4 is connected to the output terminal of the output transistor 3 (the collector of the emitter-grounded pnp transistor 3), and the normally-closed contact NC is connected to an external output terminal 5. Accordingly, by operating the relay 4 in a conduction driving state, the time-series pulse signal, formed by passing the pulse signals outputted from control devices 1 a and 1 b through the logical OR circuit (transistors 2 a and 2 b) to combine them into a single signal, is transmitted from the output transistor 3 though the normally-open contact NO of relay 4 to a reception module B.

Incidentally, the conduction of the electromagnetic coil L of relay 4 is controlled by a relay driving circuit, comprised of two transistors 6 and 7 that receive a relay driving signal from series-connected control devices 1 a and 1 b and are driven in a conducting state. Accordingly, the relay 4 is driven via the relay driving circuit (transistors 6 and 7) only when the control devices 1 a and 1 b output relay driving signals simultaneously. Also, if at least one of the control devices 1 a and 1 b halts outputting the relay driving signal, the driving of the relay 4 will be halted.

The common control module 14 is also comprised of a transistor 9 that functions as a monitoring circuit for monitoring pulse signals output externally through the normally-open contact NO of relay 4, and a transistor 8 that functions as a monitoring circuit for monitoring the pulse signals expected to appear at the normally-closed contact NC of relay 4 when the relay 4 is in a non-driven state. Then, the detected pulse signals that pass through transistors 8 and 9 (monitoring circuits) are fed as output monitoring results in1 and in to each control device 1 a and 1 b, and are used in the self-diagnostic functions of the common control module 14.

Moreover, the combustion zone control module 15 is configured so as to detect pulse signals (acknowledge signals) that are sent, as described above, from a transmission module A via a photocoupler comprised of a light emitting element 21 and a light receiving element 22 that is optically coupled to the light emitting element 21. Also, the output from the photocoupler is fed to two control devices 23 and 24 provided in a parallel configuration to double-check the reception of the pulse signals (acknowledge signals). Incidentally, each control device 23 and 24 is configured so as to recognize pulse signals having durations equal to or longer than a certain fixed interval (such as 500 ms, for example) as acknowledge signals. In other words, if the duration of the pulse signal is less than a certain fixed interval (such as 500 ms, for example), the control devices 23, 24 judges that the acknowledge signal has disappeared or that, due to some sort of abnormality in the transmission module A, the acknowledge signal has not been sent.

With a transmission system for control signals configured as described above, if the relay 4 and all other elements in the common control module 14 are functioning normally, the two control devices (CPUs) 1 and 2 provided in a parallel configuration will alternately output pulse signals of a certain fixed duration as shown in FIG. 3, for example, in response to the input of interlock signals. However, until the confirmation that the common control module 14 is functioning normally, the control devices 1 and 2 do not drive the relay 4. Accordingly, after the pulse signals outputted from each control device 1 and 2 pass through the logical OR circuit (transistors 2 a and 2 b) and are combined into a single time-series pulse signal as described above, that signal is simply supplied from the output transistor 3 to the relay 4.

However, if the relay 4 is functioning normally, when the relay 4 is not being driven, pulse signals will be outputted from the normally-closed contact NC side of relay 4 and there will be no output from the normally-open contact NO side. The result, as shown in FIG. 2, is that pulse signals detected from the normally-closed contact NC side of the relay 4 are input into the 1^(st) monitoring input port in1 of the control devices 1 and 2, and no pulse signals are input into the 2^(nd) monitoring input port in2. Based on such monitoring results, the control devices 1 and 2 each judge that the relay 4 is functioning normally, and at this time, issue a drive signal to the relay 4.

Then, when transistors 6 and 7 of the relay drive circuit that receives these relay drive signals enter into conduction mode operation, the relay 4 is driven and the output contact is switched. The result, as shown in FIG. 3, is that the time-series pulse signal formed into a single signal is now sent from the normally-open contact NO side of the relay 4, via an external contact terminal 5, to the reception module B side. At this time, there is no pulse signal output from the normally-closed contact NC side of the relay 4. In other words, the inputting of a pulse signal to the 1^(st) monitoring input port in1 in each of the control devices 1 and 2 is discontinued, and instead, a pulse signal is input to the 2^(nd) monitoring input port in2. The control devices 1 and 2, based on this type of monitoring results, judge that the relay 4 is functioning normally.

Then, at this time, because the pulse signal outputted via the external connection terminal 5 to the combustion zone control module 15 has been formed by combining the pulse signals generated alternately by the control devices 1 and 2 into a single continuous pulse signal string, this pulse signal takes on the significance of the aforementioned control signal (common control signal). Accordingly, a common control signal will not be unintentionally output from the common control module 14.

Furthermore, in the case where either control device 1 or 2 does not function normally to generate a pulse signal, or in the case of an abnormality in transistors 2 a and 2 b, which function as a pulse signal synthesis unit, a single combined time-series pulse signal string will not be generated as described above. Accordingly, in such a case, the system will judge that an abnormality has occurred at one of the control devices 1 and 2, and then the generation of pulse signals will be halted. Similarly, in the case where a pulse signal is not detected, regardless of whether the control devices 1 and 2 have been activated, the system will judge that some abnormality has occurred.

However, contact failures in the relay 4 occur are solely caused by electrical discharges that cause the contacts to fuse together when the relay 4 is being driven. Accordingly, to detect a failure of the relay 4, the driving of relay 4 is halted, and at that time, the monitored status of the 1^(st) and 2^(nd) monitoring input ports in1 and in2 may be checked. Specifically, in the case where the common contact C and the normally-open contact NO of the relay 4 are fused together, even if the driving of relay 4 has been halted, the moveable armature thereof will not return to the normally-closed contact NC side. Accordingly, in this case, as shown in FIG. 4, despite having halted the driving of relay 4 having, pulse signals continue to be output to the normally-open contact NO side of relay 4 (1^(st) monitoring input port in2) and meanwhile, no pulse signals appear on the normally-closed contact NC side of relay 4 (1^(st) monitoring input port in1).

Accordingly, as a result of such monitoring results, each of the control devices 1 and 2, judges that an abnormality has occurred in the relay 4, and for example, halts the generation of pulse signals. The result is that the transmission of pulse signals to the combustion zone control module 15 is forcibly terminated. In particular, even in the case where the driving of the relay 4 has been halted in order to terminate the outputting of pulse signals, if there is an abnormality in the relay 4, the termination of the generation of pulse signals by the control devices 1 and 2 will prohibit the subsequent outputting of pulse signals to the combustion zone control module 15.

Furthermore, in one mode of failure of the relay 4, in addition to the fusing together of the common contact C and the normally-open contact NO, the normally-closed contact NC may also become fused at the same time. When this type of situation arises, regardless of whether the relay 4 is being driven or has been halted, as shown in FIG. 5, pulse signals continue to be output to the normally-open contact NO side (monitoring input port in2) of relay 4 and pulse signals also appear on the normally-closed contact NC side (monitoring input port in1) of relay 4. Accordingly, even when these types of monitoring results are obtained, each control device 1 and 2 may be configured to judge that an abnormality has occurred in the relay 4, halt the generation of the pulse signals, and to terminate forcibly the transmission of pulse signals to the combustion zone control module 15.

Namely, as described above, with the common control module 14 comprising an output section for control signals, in the state where two control devices 1 and 2 alternately generate pulse signals, by controlling the driving of the relay 4 so as to enable or disable operation of the burner, during normal operation, while the burner operation is enabled, pulse signals are detected only at the normally-open contact NO side (monitoring input port in2) of relay 4, but while the burner operation is disabled, pulse signals are detected only at the normally-closed contact NC side (monitoring input port in1), and therefore the common control module 14 is able to detect the occurrence of other states as the occurrence of an abnormality. Thus, when an abnormality is detected, the control devices 1 and 2 disable the generation of pulse signals so that there is no transmission of mistaken control signals to the combustion zone control module 15.

Furthermore, in the case where an abnormality has occurred in either one of the two control devices 1 and 2, the outputting of pulse signals is discontinued from the control device side where the abnormality occurred. Accordingly, even if fed through a logical OR circuit (transistors 2 a and 2 b) to form a time-series string of pulse signals, the output thereof will consist only of the pulse signals outputted from the one control device. Accordingly, the abnormal condition of the other control device can be detected based on the occurrence of intermittent interruptions of a certain fixed period in the pulse signal. Thus, in this case, prohibiting the generation of pulse signals by the normally functioning control device enables the outputting of mistaken pulse signals from the common control module 14 to be prevented reliably.

Also, with the aforementioned configuration, a single continuous time-series pulse signal cannot be obtained if the transistors 2 a and 2 b were to fail. Also, the relay 4 cannot be switched on and off if the transistors 6 and 7 were to fail. Accordingly, by monitoring the signal detected at the monitoring input ports in1 and in2, the above-described abnormalities can also be detected. Therefore, only when the common control module 14 is functioning normally, common control signals that are continuous pulse signals having durations equal to or longer than a certain fixed interval can be reliably transmitted to the combustion zone control module 15. Moreover, the transmission of acknowledge signals (zone control signals) from the combustion zone control module 15 to the burner control module 16 may be implemented similarly.

Furthermore, the present invention is not limited to the above-described embodiment. For example, the interlock may be configured in accordance with the specifications of the combustion furnace, or an appropriate interlock can be added. Also, in the above-described embodiment and FIG. 1, a configuration was shown in which a combustion control apparatus (BCU) 13 was individually provided for each burner 11, but the invention is not limited to this configuration, and may also be configured with two or more burners 11 associated with a single combustion control apparatus 13. In this case, all burners 11 associated with a single combustion control apparatus 13 are provided in the same zone, that is to say, the burners 11 are preferably limited to the same operating conditions. Even in this type of situation, it is sufficient to judge the interlock at each hierarchical level classified as described above. Also, in order to ensure operational reliability of the transmission of signals among modules, it goes without saying that various measures may be implemented. Additionally, the present invention, without departing from the gist thereof, may be modified variously and implemented. 

1. A combustion furnace control apparatus, comprising: a common control module verifying the state of a 1^(st) interlock pertaining to the safe operation of the entire combustion furnace, outputting common control signals required for the safe operation of the combustion furnace, and controlling the overall operation of the combustion furnace; and a combustion zone control module, provided in correspondence to a combustion zone provided with a burner, verifying the state of a 2^(nd) interlock pertaining to the combustion environment in said combustion zone and common control signals outputted from the common control module, and controlling the operation of the burner in said combustion zone; wherein said common control module and said combustion zone control module are provided in a hierarchical configuration.
 2. A combustion furnace control apparatus as cited in claim 1, wherein the combustion furnace comprises a plurality of combustion zones each being provided with one or a plurality of burners; and a combustion zone control module is provided in correspondence to each of the respective combustion zones.
 3. A combustion furnace control apparatus, comprising: a common control module for verifying the state of a 1^(st) interlock pertaining to the safe operation of a combustion furnace, outputting common control signals required for the operation of the combustion furnace, and controlling the overall operation of the combustion furnace; and a combustion zone control module, provided in correspondence to a combustion zone provided with a burner, for verifying the state of a 2^(nd) interlock pertaining to the combustion environment in said combustion zone and common control signals outputted from the common control module, controlling the safe operation environment of said combustion zone, and outputting combustion zone control signals required for operation of the burner provided in said combustion zone; and a burner control module, provided in correspondence to the burner, for verifying the state of a 3^(rd) interlock pertaining to inherent safe operation in said burner and combustion zone control signals outputted from the combustion zone control module, and for controlling the operation of said burner; wherein said common control module, said combustion zone control module and said burner control module are provided in a hierarchical configuration.
 4. A combustion furnace control apparatus as cited in claim 3, wherein the combustion furnace comprises a plurality of combustion zones each being provided with one or a plurality of burners; the combustion zone control module is provided in correspondence to each of the respective combustion zones; and the burner control module is provided in correspondence to each of the burners.
 5. A combustion furnace control apparatus as cited in claim 1, wherein the common control module outputs signals, as common control signals, for enabling or disabling the operation of a burner provided in the combustion furnace.
 6. A combustion furnace control apparatus as cited in claim 1, wherein when the burner operation is enabled, the combustion zone control module ventilates said combustion zone, prepares a safe operating environment for the burner in said combustion zone, and after the safe operating environment of said combustion zone has been prepared, outputs the combustion zone control signals.
 7. A combustion furnace control apparatus as cited in claim 1, wherein combustion control of the burner is implemented by a combustion control device provided in correspondence to said burner, and only when a combustion zone control signal has been received from the combustion zone control module and operation has been enabled, said burner is operated according to combustion control implemented by the combustion control device.
 8. A combustion furnace control apparatus as cited in claim 3, wherein combustion control of the burner is implemented by a combustion control device provided in correspondence to said burner, and only when operation has been enabled by a burner control module that has verified the combustion zone control signal from the combustion zone control module and the state of the 3^(rd) interlock, said burner is operated according to combustion control implemented by the combustion control device.
 9. A combustion furnace control apparatus as cited in claim 3, wherein the common control module outputs signals, as common control signals, for enabling or disabling the operation of a burner provided in the combustion furnace.
 10. A combustion furnace control apparatus as cited in claim 3, wherein when the burner operation is enabled, the combustion zone control module ventilates said combustion zone, prepares a safe operating environment for the burner in said combustion zone, and after the safe operating environment of said combustion zone has been prepared, outputs the combustion zone control signals. 